Police in the northern province of Bac Giang have arrested six people for causing disorder at the provincial authorities' headquarters, an official said Monday.

Related agencies are also investigating the death of Nguyen Van Khuong that triggered the protest involving thousands of people, Bui Van Hai, vice chairman of the Bac Giang People's Committee, told the press.

At around 6 p.m. on July 23, Khuong, 21, was riding with Pham Thi Ngoan on a motorbike when he was stopped by traffic police in Tan Yen District for violations, Hai quoted the police report as saying.

Police then took the couple and the bike to the station for writing up the fine.

Shortly after 7 p.m. Khuong showed signs of abnormal health conditions, prompting the police to rush him to the Tan Yen District General Hospital, where he died later, Hai said.

Tan Yen police handed over Khuong's body to his family at 2.30 a.m. on July 24, and said they were co-operating with provincial police to investigate the death as requested by the family, he added.

However, at around 1 p.m. the day after, some people in the procession to a local graveyard brought the coffin to the Bac Giang People's Committee headquarters, and thousands joined the protest, the vice chairman said.

It was only around 5 p.m. that Khuong's family brought the coffin back for funeral after being persuaded by the authorities.